Abundant low-level moisture and stagnant conditions combined to produce widespread, dense fog Thursday in low-lying areas of Utah, Salt Lake, Davis, Box Elder, Tooele and Cache counties.

The fog, which greatly hampered flying conditions Wednesday night and early Thursday at Salt Lake International Airport, was extremely dense in some areas.The fog had thinned out a bit in some areas by midmorning Thursday, said William J. Alder, meteorologist in charge of the Salt Lake office of the National Weather Service.

But Alder said foggy conditions, which apparently were a factor in the rollover of a semitrailer truck into the median of I-15 near Lindon, Utah County, about 4:30 a.m., are expected to continue during the early morning and evening hours through Saturday.

A Utah Highway Patrol dispatcher said the driver of the semi suffered only minor injuries.

At 10:30 a.m. visibility was vacillating between zero and a quarter of a mile at the airport, Alder said.

Frank Ratliff, operations manager at the airport, said fog conditions were horrible early Thursday.

He said operations vehicles had to escort planes off the runway and to the airport gates at 7:30 a.m.

Air traffic was at a standstill for a few minutes about 10 a.m., Ratliff said. By 10:30 planes were able to land and take off at the airport, but Ratliff said the fog didn't seem to be dissipating.

Fog-seeding operations didn't begin until 7 a.m. because of mechanical problems with a fog-seeding aircraft earlier, Ratliff said.

Barken International has a contract for fog dispersal at the airport.

The Deseret News received a report that several inbound Delta Air Lines flights were unable to land at Salt Lake International Wednesday night.

Fred Rollins, Delta marketing director, said Thursday morning he could not give an accurate figure on the number of flights diverted. He said some flights were rerouted to Idaho Falls, Idaho, with some airline passengers bused to Salt Lake City. Others returned to Salt Lake City by air after 11 p.m. Wednesday, he said.

Pam American World Airways flight 567, a 727 jet carrying 51 passengers from Minneapolis, was scheduled to land at the airport at 9:47 p.m. Wednesday. But after circling the airport and other northern Utah cities for some time, the plane landed at Hill Air Force Base.

Elizabeth Manners, a Pan Am spokeswoman in New York City, said the plane landed at HAFB because that was the only airport available. The Provo and Boise airports also were socked in with fog, she said.

Manners said a report that the plane had run out of fuel was not true. But she said the plane was refueled before continuing on to Salt Lake City. The plane landed at Salt Lake International at 12:50 a.m. Thursday.

Despite problems at the airport, foggy conditions had their side benefits. One Utah Highway Patrol dispatcher said dispatchers hadn't received a report of a single accident along the freeways in Salt Lake County as of 8:25 a.m. Motorists were apparently forced to drive very slowly.

Alder said a dense fog advisory has been issued for the northern Wasatch Front and the Cache Valley.

Fog dispersal activities in the area around the airport caused roads to become very slick in the vicinity of the airport. Commuters needed extra time to reach their destinations, said forecaster Michael C. Conger.

Alder said little change in stagnant conditions is expected through Saturday.

By Sunday at least parts of the state may receive new snowfall, but the storm doesn't appear very strong, Alder said.

"But hopefully, it will be enough to start stirring things around some. We ought to see a little more improvement by Monday. It looks like we'll get light amounts of snow on Sunday and into early Monday in northwestern Utah and the northern mountains," Alder said.